Current treatment of severe acute respiratory failure (ARF) relies on intubation and mechanical ventilation to improve arterial oxygenation and carbon dioxide release, to decrease the work of breathing and the adverse effects therefrom, and to provide access for tracheal suctioning. This often leads to tracheal injury, tracheal aspiration, decreased tracheal mucus velocity, barotrauma, and a high incidence of nosocomial pneumonia. We have further improved our new method of minimally invasive passive ventilation that dispenses with tracheal intubation and the use of mechanical ventilation: Spontaneous Airway Pressure Release Ventilation (S-APRV), in which all air/oxygen is delivered to the level of the carina through a small Reverse-Thrust Catheter (RTC), at the level of the carina. We now include in S-APRV a mechanism to provide for a brief (one second or less) timed period in the respiratory cycle during which air/oxygen delivery is transiently increased to allow for more rapid inflation of the lungs - particularly useful in large animals (and in adult man). In studies in sheep with severe ARF following intravenous infusion of oleic acid droplets (mean size, about 220 micrometers) at a total dose of 100 mg/kg, we can reproducibly and consistently induce severe ARF in sheep. In studies currently in progress, we treat such sheep with ARF in one of three ways: 1. Pressure support ventilation through a standard tracheostomy tube, PEEP 5 cm H2O, pressure support 10 cm H2O; 2. CPAP of 5 cm H2O, using a standard tracheostomy tube; and 3. S-APRV, using a minitracheostomy tube, with a RTC catheter. Our preliminary results show that overall, recovery in gas exchange proceeded comparably in the three groups. Sheep in groups 1 and 2 required frequent tracheal aspiration to avoid obstruction to air flow, whereas sheep on S-APRV did not require tracheal suctioning at any time, because of the self-cleaning feature of the RTC catheter. To date, these studies suggest that with S-APRV tracheal intubation can likely be avoided as there appears to be spontaneous removal of secretions from the upper major airways through the effects of the RTC catheter gas flow. We conclude from results of our studies to date that such a method is likely to lead to greatly improved quality of care for ARF patients with a reduction in nosocomial pneumonia (as there is no need for tracheal intubation or tracheal suctioning). In addition, the patient will likely retain the ability to vocalize, swallow, and ingest food and fluid orally.